Visualization of Path Expressions in a Virtual Object-Oriented Database Query Language

  • Authors:

  • Jeonghee Kim;Taisook Han;Suk Kyoon Lee

  • Affiliations:

  • -;-;-

  • Venue:
  • DASFAA '99 Proceedings of the Sixth International Conference on Database Systems for Advanced Applications
  • Year:
  • 1999

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Abstract

Path expressions have been accepted for concisely manipulating the nested structures in complex object-oriented query expressions. However, previous visual query languages hardly represent such query expressions in a concise and intuitive way partly due to improper visual representation of path expressions and partly due to lack of well-defined syntax and semantics of languages. In this paper, we present visual modeling of path expressions in a visual object-oriented database query language called Visual Object-Oriented Query Language (VOQL) which has excellent expressive power for sets, simple and intuitive syntax, and well-defined semantics. This is enabled by explicitlySpecifying the semantics of multi-valued path expressions based on the visual notation capable of representing set relationships in addition to functional relationships. The basic visual constructs called blobs and nested blobs denote sets of objects that path expressions represent while the constructs called binding edges and flattening edges visually simulate the notions of variable binding and dot functions in path expressions respectively. Based on the constructs, the grammer of VOQL defines the syntactic components while the semantics of query expressions are provided by syntax-directed translation to the counterparts in the extended relational calculus. Also, the visual constructs allow modeling of restricted universal quantification with a visual scoping box and effectively represent nested quantification and recursive queries without semantic ambiguities. An explicit specification of the semantics of multi-valued path expressions in a concise and unified visual notation is new and visually clarifies the semanticsof quantified queries in the nested structures.